High temperature tensile experiments were carried out to investigate the effect of hydrogen on the superplastic deformation behavior of Ti-6Al-4V titanium alloy.The influence of hydrogen on the microstructure evolution of the alloy was analyzed by OM,SEM,TEM,and XRD.The results show that the amount of β phase in the hydrogenated alloy increases with increasing hydrogen content,and martensite begins to form while the mass content of hydrogen reaches to 0.2% and becomes coarser with the increase in hydrogen content.A reasonable hydrogen content can improve the superplastic behavior such as increasing the m value and lowering the flow stress and temperature.The addition of 0.1% hydrogen in Ti-6Al-4V alloy can result in a decrease in peak flow stress of 53% and a decrease in deformation temperature of 60 ℃.Due to addition of hydrogen the dislocation density of the hydrogenated alloy after deformation is lower than that of the unhydrogenated alloy.